Successive interference canceling for CDMA

ABSTRACT

Successive interference canceling for CMDA. ICI may result from a signal&#39;s multi-path effects, or by filtering/suppression of some of the component energy of the signaling waveforms. Energy component attenuation destroys orthogonality of CDMA symbols thereby causing ICI. An ICF suppresses frequency domain portions (attenuates ingress), but also introduces ICI. Following the ICF, the signal is de-spread sliced, re-spread and convolved with the ICF echoes (except first tap echoes). Convolving re-spread hard decisions with delayed ICF taps is equivalent to partially re-modulating the first-pass hard decisions to efficiently “add-back-in” the signal energy which was blanked/subtracted by the ICF. Alternatively, parameter estimation de-rotates and re-rotates soft symbols and hard decisions, respectively compensating for undesirable symbol rotation. The convolved signal is subtracted from a delayed version of the ICF output signal. If desired, this process may be repeated successively to enhance the accuracy of the obtained data decisions in the next stage

CROSS REFERENCE TO RELATED PATENTS/PATENT APPLICATIONS

Continuation priority claim, 35 U.S.C. §120

The present U.S. Utility Patent Application claims priority pursuant to35 U.S.C. §120, as a continuation, to the following U.S. Utility PatentApplication which is hereby incorporated herein by reference in itsentirety and made part of the present U.S. Utility Patent Applicationfor all purposes:

1. U.S. Utility application Ser. No. 10/242,032, entitled “SUCCESSIVEINTERFERENCE CANCELING FOR CMDA,” (Attorney Docket No. BP2161), filedSep. 12, 2002, pending.

Parent's CIP and Provisional priority claims, 35 U.S.C. §120, 119(e)

The U.S. Utility application Ser. No. 10/242,032 claims prioritypursuant to 35 U.S.C. §119(e) to the following U.S. Provisional PatentApplication which is hereby incorporated herein by reference in itsentirety and made part of the present U.S. Utility Patent Applicationfor all purposes:

2. U.S. Provisional Application Ser. No. 60/394,893, entitled“SUCCESSIVE INTERFERENCE CANCELING FOR CMDA,” (Attorney Docket No.BP2161), filed Jul. 10, 2002; and

The U.S. Utility application Ser. No. 10/242,032 also claims prioritypursuant to 35 U.S.C. §120, as a continuation-in-part (CIP), to thefollowing U.S. Utility Patent Application which is hereby incorporatedherein by reference in its entirety and made part of the present U.S.Utility Patent Application for all purposes:

3. U.S. Utility application Ser. No. 10/136,059, entitled “CHIP BLANKINGAND PROCESSING IN S-CDMA TO MITIGATE IMPULSE AND BURST NOISE AND/ORDISTORTION,” (Attorney Docket No. BP2058), filed Apr. 30, 2002, pending,which claims priority pursuant to 35 U.S.C. §120, as acontinuation-in-part (CIP), to the following U.S. Utility PatentApplication which is hereby incorporated herein by reference in itsentirety and made part of the present U.S. Utility Patent Applicationfor all purposes:

4. U.S. Utility application Ser. No. 10/000,415, entitled “Detection andmitigation of temporary impairments in a communications channel,”(Attorney Docket No. 13199US02), filed Nov. 02, 2001, pending, whichclaims priority pursuant to 35 U.S.C. §119(e) to the following U.S.Provisional Patent Application which is hereby incorporated herein byreference in its entirety and made part of the present U.S. UtilityPatent Application for all purposes:

5. U.S. Provisional Application Ser. No. 60/296,884, entitled “Detectionand mitigation of temporary impairments in a communications channel,”(Attorney Docket No. 13199US01), filed Jun. 08, 2001.

BACKGROUND OF THE INVENTION

1. Technical Field of the Invention

The invention relates generally to communication systems; and, moreparticularly, it relates to communication receivers employing CodeDivision Multiple Access (CDMA).

2. Description of Related Art

Data communication systems have been under continual development formany years. One particular type of communication system, a cable modem(CM) communication system, has been under continual development for thelast several years. There has been development to try to provide forimprovements in the manner in which communications between the CM usersand a cable modem termination system (CMTS) is performed. Many of theseprior art approaches seek to perform and provide broadband networkaccess to a number of CM users.

CM communication systems are realized when a cable company offersnetwork access, oftentimes Internet access, over the cable. This way,the Internet information can use the same cables because the CMcommunication system puts downstream data, sent from the Internet to anindividual computer having CM functionality, into a communicationchannel having a 6 MHz capacity. The reverse transmission is typicallyreferred to as upstream data, information sent from an individual backto the Internet, and this typically requires even less of the cable'sbandwidth. Some estimates say only 2 MHz are required for the upstreamdata transmission, since the assumption is that most people download farmore information than they upload.

Putting both upstream and downstream data on the cable television systemrequires two types of equipment: a cable modem on the customer end andthe CMTS at the cable provider's end. Between these two types ofequipment, all the computer networking, security and management ofInternet access over cable television is put into place. Thisintervening region may be referred to as a CM network segment, and avariety of problems can occur to signals sent across this CM networksegment.

One particular deficiency that may arise in this CM network segment isthe introduction of multi-path effects where there is interference fromone symbol to another in a delayed, scaled form. For example, a scaledand delayed version of one symbol is undesirably added to other symbols.This can lead to significant degradation in performance. In CDMAsystems, these multi-path effects can be totally deficient, in that, itmay make accurate decoding of the transmitted data virtually impossible.A number of sources may create these multi-path effects, including thecommunication channel itself, as well as notch filters and interferencecanceling filters within a communication receiver that may seek tominimize the deleterious effects of a communication channel.

In synchronous code division multiple access (S-CDMA) systems, severalcable modems (CMs) transmit their signals such that these signals arereceived at the CMTS on the same frequency and at the same time. Inorder for different CM signals to be separated at the CMTS, each CMspreads its data sequence by a code sequence of wider spectrum. The CMTSreceives the sum of all CM signals. To separate a specific CM signal,the CMTS despreads the received sequence by multiplying it with the codesequence of the desired CM.

In order to minimize the inter-code-interference (ICI), the spreadingcodes are chosen such that they are perfectly orthogonal, when they arereceived in perfect synchronism. In order to guarantee codeorthogonality, the code sequences are often chosen to have cyclic-shiftproperties. To preserve the code orthogonality at the CMTS, transmitequalizers are used by CMs to guarantee a perfect single-path overallchannel seen at the CMTS. The transmit equalizer taps at a specific CMare usually set according to an estimate of the channel between the CMand CMTS, which is estimated during the ranging process.

In many cases, the received signal at the CMTS is corrupted with strongnarrow-band interference (or ingress). An interference canceling filter(ICF) is used to notch out ingress before signal despreading. Althoughthis ICF can mitigate ingress, it can cause considerable performancedegradation, which can be explained as follows. The ICF taps causeinter-symbol-interference (ISI) as they can be viewed as echoes to thesignal. These echoes result in shifted (or delayed) replica of thereceived signal at the CMTS side. This enhances ICI as codes loose theirperfect orthogonality. Moreover, due to the cyclic-shift properties ofthe used orthogonal codes, a shifted replica of one code might resembleanother code to a great extent, which enhances the ICI significantly.The same effect can also be caused by imperfections in the channelestimation ranging process, possible channel variations, as well as thefinite length and precision of the transmit equalizers, all of which canresult in residual echoes in the overall channel seen at the CMTS. Theproblems described herein may arise within a variety of contexts,including both wireless and wired communication systems.

The effect of ISI in CDMA systems can be extremely problematic and istypically very severe in its magnitude and nature. Because theneighboring codes are typically orthogonal to one another, the ISI lookvery similar to delayed (shifted and scaled) versions of one another.This interference can be highly correlated and very problematic.

Within Time Division Multiple Access (TDMA) communication systems, acommon approach to deal with ISI is to employ a Decision FeedbackEqualizer (DFE) type structure. This DFE structure can compensate forinterference that takes the form described above that is delayed by atleast one symbol. For example, before decoding a second symbol in TDMAusing DFE, a scaled version of the first symbol is subtracted thereform. The scaling is based on the determined characterization of the ISIthat is attributed to the second symbol from the first symbol.

Within the CDMA context, there is no such way known in the prior art todeal with these effects of multi-path and ISI is a satisfactory way. Inthe CDMA context, a signal is spread out over a number of chips. Here,the ISI will vary on a chip by chip basis. When narrowband interferenceis undesirably added to these various chips it makes the decoding of thesignal nearly impossible. This is because all of the chips need to bereceived to perform the soft decisions that are used later to make harddecisions there from. For example, in an embodiment where N chips areused to perform symbol decisions, then all of the 128 chips are neededto N chips need to be received before making the symbol decisions of thesymbols contained and coded therein. The interference between thesechips will be non-causal in the CDMA context. The very manner in which aCDMA receiver performs decoding of its signals is what makes itimpossible to use a DFE type structure (as in TDMA) to perform thedecoding. Within CDMA, a clean representation of all of the chips mustbe achieved. The very way that a CDMA signal is received will inherentlyinclude (in the existence of ISI on the chip level) of one clean chipwith the remaining chips having the ISI. Since CDMA does not decode asingle chip at a time (whereas TDMA may decode a single symbol at atime), this need to decode all of the chips together over a relativelylong period of time, for many codes, and sum over all of those codes todecode each symbol. Basically, the fact that, in CDMA, many symbols areall decoded at the same time, there is a need for a clean representationof all of the chips of a received signal.

BRIEF SUMMARY OF THE INVENTION

The present invention is directed to apparatus and methods of operationthat are further described in the following Brief Description of theSeveral Views of the Drawings, the Detailed Description of theInvention, and the claims. Other features and advantages of the presentinvention will become apparent from the following detailed descriptionof the invention made with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a system diagram illustrating an embodiment of a cable modem(CM) communication system that is built according to the invention.

FIG. 2 is a system diagram illustrating another embodiment of a CMcommunication system that is built according to the invention.

FIG. 3 is a system diagram illustrating an embodiment of a cellularcommunication system that is built according to the invention.

FIG. 4 is a system diagram illustrating another embodiment of a cellularcommunication system that is built according to the invention.

FIG. 5 is a system diagram illustrating an embodiment of a satellitecommunication system that is built according to the invention.

FIG. 6 is a system diagram illustrating an embodiment of a microwavecommunication system that is built according to the invention.

FIG. 7 is a system diagram illustrating an embodiment of apoint-to-point radio communication system that is built according to theinvention.

FIG. 8 is a system diagram illustrating an embodiment of a highdefinition television (HDTV) communication system that is builtaccording to the invention.

FIG. 9 is a system diagram illustrating an embodiment of a communicationsystem that is built according to the invention.

FIG. 10 is a system diagram illustrating another embodiment of acommunication system that is built according to the invention.

FIG. 11 is a system diagram illustrating an embodiment of a cable modemtermination system (CMTS) system that is built according to theinvention.

FIG. 12 is a system diagram illustrating an embodiment of a burstreceiver system that is built according to the invention.

FIG. 13 is a system diagram illustrating an embodiment of a Bluetooth™communication system that is built according to the invention.

FIG. 14 is a functional block diagram illustrating an embodiment ofsuccessive interference canceling (SIC) functionality for CDMA that isarranged according to the invention in a parallel implementation.

FIG. 15 is a functional block diagram illustrating an embodiment of SICfunctionality for CDMA that is arranged according to the invention in aserial implementation.

FIG. 16 is a diagram illustrating the effects of rotation on symbolscoded using a constellation of QPSK (Quadrature Phase Shift Keying)modulation.

FIG. 17 is a diagram illustrating the effects of rotation on symbolscoded using a constellation of 8 PSK (8 Phase Shift Keying) modulation.

FIG. 18 is a diagram illustrating the effects of rotation on symbolscoded using a constellation of 16 QAM (Quadrature Amplitude Modulation)modulation.

FIG. 19 is a diagram illustrating the effects of rotation on symbolscoded using a constellation of 16 APSK (Amplitude Phase Shift Keying)modulation.

FIG. 20 is a functional block diagram illustrating an embodiment ofsuccessive interference canceling (SIC) functionality for CDMA that isarranged according to the invention in a parallel implementation that isoperable to compensate for rotation.

FIG. 21 is a functional block diagram illustrating an embodiment of SICfunctionality for CDMA that is arranged according to the invention in aserial implementation that is operable to compensate for rotation.

FIG. 22 is an operational flow diagram illustrating an embodiment of anSIC method for CDMA that is performed according to the invention.

FIG. 23 is an operational flow diagram illustrating another embodimentof an SIC method for CDMA that is performed according to the invention.

FIG. 24 is a diagram illustrating a number of considerations of whichiteration(s) to perform rotation correction according to the invention.

FIG. 25 shows an embodiment of SIC for CDMA simulation results accordingto the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a system diagram illustrating an embodiment of a CMcommunication system 100 that is built according to the invention. TheCM communication system includes a number of CMs (shown as being used bya CM user #1 111, a CM user #2 115, . . . , and a CM user #n 121) and aCMTS 130. The CMTS 130 is a component that exchanges digital signalswith CMs on a cable network.

Each of a number of CM users (shown as the CM user #1 111, the CM user#2 115, . . . , and the CM user #n 121) is operable to communicativelycouple to a CM network segment 199. A number of elements may be includedwithin the CM network segment 199. For example, routers, splitters,couplers, relays, and amplifiers may be contained within the CM networksegment 199 without departing from the scope and spirit of theinvention.

The CM network segment 199 allows communicative coupling between a CMuser and a cable headend transmitter 120 and/or a CMTS 130. In someembodiments, a cable CMTS is in fact contained within a headendtransmitter. In other embodiments, a cable CMTS is located externallywith respect to a headend transmitter. For example, the CMTS 130 may belocated externally to the cable headend transmitter 120. In alternativeembodiments, a CMTS 135 may be located within the cable headendtransmitter 120. The CMTS 130 may be located at a local office of acable television company or at another location within a CMcommunication system. In the following description, the CMTS 130 is usedfor illustration; yet, the same functionality and capability asdescribed for the CMTS 130 may equally apply to embodiments thatalternatively employ the CMTS 135. The cable headend transmitter 120 isable to provide a number of services including those of audio, video,local access channels, as well as any other service known in the art ofcable systems. Each of these services may be provided to the one or moreCM users 111,115, . . . , 121.

In addition, through the CMTS 130, the CM users 111, 115, . . . , 121are able to transmit and receive data from the Internet, . . . , and/orany other network to which the CMTS 130 is communicatively coupled. Theoperation of a CMTS, at the cable-provider's head-end, may be viewed asproviding analogous functions provided by a digital subscriber lineaccess multiplexor (DSLAM) within a digital subscriber line (DSL)system. The CMTS 130 takes the traffic coming in from a group ofcustomers on a single channel and routes it to an Internet ServiceProvider (ISP) for connection to the Internet, as shown via the Internetaccess. At the head-end, the cable providers will have, or lease spacefor a third-party ISP to have, servers for accounting and logging,dynamic host configuration protocol (DHCP) for assigning andadministering the Internet protocol (IP) addresses of all the cablesystem's users (CM users 111, 115, . . . , 121), and typically controlservers for a protocol called Data Over Cable Service InterfaceSpecification (DOCSIS), the major standard used by U.S. cable systems inproviding Internet access to users. The servers may also be controlledfor a protocol called European Data Over Cable Service InterfaceSpecification (EuroDOCSIS), the major standard used by European cablesystems in providing Internet access to users, without departing fromthe scope and spirit of the invention.

The downstream information flows to all of the connected CM users 111,115, . . . , 121. The individual network connection, within the CMnetwork segment 199, decides whether a particular block of data isintended for it or not. On the upstream side, information is sent fromthe CM users 111, 115, . . . , 121 to the CMTS 130; on this upstreamtransmission, the users within the CM users 111, 115, . . . , 121 towhom the data is not intended do not see that data at all. As an exampleof the capabilities provided by a CMTS, the CMTS will enable as many as1,000 users to connect to the Internet through a single 6 MHz channel.Since a single channel is capable of 30-40 megabits per second of totalthroughput, this means that users may see far better performance than isavailable with standard dial-up modems. Some embodiments implementingthe invention are described below and in the various Figures that showthe data handling and control within one or both of a CM and a CMTSwithin a CM system that operates by employing S-CDMA (Synchronous CodeDivision Multiple Access).

The CM users 111, 115, . . . , 121 and the CMTS 130 communicatesynchronization information to one another to ensure proper alignment oftransmission from the CM users 111, 115, . . . , 121 to the CMTS 130.This is where the synchronization of the S-CDMA communication systems isextremely important. When a number of the CMs all transmit their signalsat a same time such that these signals are received at the CMTS 130 onthe same frequency and at the same time, they must all be able to beproperly de-spread and decoded for proper signal processing.

Each of the CMs users 111, 115, . . . , 121 is located a respectivetransmit distance from the CMTS 130. In order to achieve optimumspreading diversity and orthogonality for the CMs users 111, 115, . . ., 121 to transmission of the CMTS 130, each of the CM transmissions mustbe synchronized so that it arrives, from the perspective of the CMTS130, synchronous with other CM transmissions. In order to achieve thisgoal, for a particular transmission cycle, each of the CMs 111, 115, . .. , 121 will typically transmit to the CMTS 130 at a respectivetransmission time, which will likely differ from the transmission timesof other CMs. These differing transmission times will be based upon therelative transmission distance between the CM and the CMTS 130. Theseoperations may be supported by the determination of the round tripdelays (RTPs) between the CMTS 130 and each supported CM. With theseRTPs determined, the CMs may then determine at what point to transmittheir S-CDMA data so that all CM transmissions will arrive synchronouslyat the CMTS 130.

The invention enables successive interference canceling. (SIC)functionality for CDMA within the CMTS 130. This SIC functionality forCDMA is shown as within a functional block 131 within the cable headendtransmitter 120. This SIC functionality for CDMA may also be supportedwithin the CMTS 135 and/or the CMTS 130, whichever may be implementedwithin a particular embodiment. All of the functionality describedherein this patent application may be performed within the context ofthe CM communication system of the FIG. 1. The FIG. 1 shows just oneembodiment where the various aspects of the invention may beimplemented. Several other embodiments are described as well.

FIG. 2 is a system diagram illustrating another embodiment of a CMcommunication system 200 that is built according to the invention. Fromcertain perspectives, the FIG. 2 may be viewed as a communication systemallowing bi-directional communication between a customer premiseequipment (CPE) 240 and a network. In some embodiments, the CPE 240 is apersonal computer or some other device allowing a user to access anexternal network. The external network may be a wide area network (WAN)280, or alternatively, the Internet 290 itself. For example, the CMcommunication system 200 is operable to allow Internet protocol (IP)traffic to achieve transparent bi-directional transfer between aCMTS-network side interface (CMTS-NSI: viewed as being between the CMTS230 and the Internet 290) and a CM to CPE interface (CMCI: viewed asbeing between the CM 210 and the CPE 240).

The WAN 280, and/or the Internet 290, is/are communicatively coupled tothe CMTS 230 via the CMTS-NSI. The CMTS 230 is operable to support theexternal network termination, for one or both of the WAN 280 and theInternet 290. The CMTS 230 includes a modulator and a demodulator tosupport transmitter and receiver functionality to and from a CM networksegment 299. The receiver functionality within the CMTS 230 is operableto support SIC functionality for CDMA 231 according to the invention.

A number of elements may be included within the CM network segment 299.For example, routers, splitters, couplers, relays, and amplifiers may becontained within the CM network segment 299 without departing from thescope and spirit of the invention. The CM network segment 299 allowscommunicative coupling between a CM user and the CMTS 230.

FIG. 3 is a system diagram illustrating an embodiment of a cellularcommunication system 300 that is built according to the invention. Amobile transmitter 310 has a local antenna 311. The mobile transmitter310 may be any number of types of transmitters including a cellulartelephone, a wireless pager unit, a mobile computer having transmitfunctionality, or any other type of mobile transmitter. The mobiletransmitter 310 transmits a signal, using its local antenna 311, to abase station receiver 340 via a wireless communication channel. The basestation receiver 340 is communicatively coupled to a receiving wirelesstower 349 to be able to receive transmission from the local antenna 311of the mobile transmitter 310 that have been communicated via thewireless communication channel. The receiving wireless tower 349communicatively couples the received signal to the base station receiver340.

The base station receiver 340 is then able to support SIC functionalityfor CDMA according to the invention, as shown in a functional block 341,on the received signal. The FIG. 3 shows just one of many embodimentswhere SIC functionality for CDMA, performed according to the invention,may be performed to provide for improved operation within acommunication system.

FIG. 4 is a system diagram illustrating another embodiment of a cellularcommunication system that is built according to the invention. Fromcertain perspectives, the FIG. 4 may be viewed as being the reversetransmission operation of the cellular communication system 300 of theFIG. 3. A base station transmitter 420 is communicatively coupled to atransmitting wireless tower 421. The base station transmitter 420, usingits transmitting wireless tower 421, transmits a signal to a localantenna 439 via a wireless communication channel. The local antenna 439is communicatively coupled to a mobile receiver 430 so that the mobilereceiver 430 is able to receive transmission from the transmittingwireless tower 421 of the base station transmitter 420 that have beencommunicated via the wireless communication channel. The local antenna439 communicatively couples the received signal to the mobile receiver430. It is noted that the mobile receiver 430 may be any number of typesof transmitters including a cellular telephone, a wireless pager unit, amobile computer having transmit functionality, or any other type ofmobile transmitter.

The mobile receiver 430 is then able to support SIC functionality forCDMA according to the invention, as shown in a functional block 431, onthe received signal. The FIG. 4 shows just one of many embodiments wherethe SIC functionality for CDMA, performed according to the invention,may be performed to provide for improved operation within acommunication system.

FIG. 5 is a system diagram illustrating an embodiment of a satellitecommunication system 500 that is built according to the invention. Atransmitter 520 is communicatively coupled to a wired network 510. Thewired network 510 may include any number of networks including theInternet, proprietary networks, . . . , and other wired networks. Thetransmitter 520 includes a satellite earth station 551 that is able tocommunicate to a satellite 553 via a wireless communication channel. Thesatellite 553 is able to communicate with a receiver 530. The receiver530 is also located on the earth. Here, the communication to and fromthe satellite 553 may cooperatively be viewed as being a wirelesscommunication channel, or each of the communication to and from thesatellite 553 may be viewed as being two distinct wireless communicationchannels.

For example, the wireless communication “channel” may be viewed as notincluding multiple wireless hops in one embodiment. In otherembodiments, the satellite 553 receives a signal received from thesatellite earth station 551, amplifies it, and relays it to the receiver530; the receiver 530 may include terrestrial receivers such assatellite receivers, satellite based telephones, . . . , and satellitebased Internet receivers, among other receiver types. In the case wherethe satellite 553 receives a signal received from the satellite earthstation 551, amplifies it, and relays it, the satellite 553 may beviewed as being a “transponder.” In addition, other satellites may exist(and operate in conjunction with the satellite 553) that perform bothreceiver and transmitter operations. In this case, each leg of anup-down transmission via the wireless communication channel would beconsidered separately. Clearly, a wireless communication channel betweenthe satellite 553 and a fixed earth station would likely be lesstime-varying than the wireless communication channel between thesatellite 553 and a mobile station.

In whichever embodiment is implemented, the satellite 553 communicateswith the receiver 530. The receiver 530 may be viewed as being a mobileunit in certain embodiments (employing a local antenna 512);alternatively, the receiver 530 may be viewed as being a satellite earthstation 552 that may be communicatively coupled to a wired network in asimilar manner that the satellite earth station 551, within thetransmitter 520, communicatively couples to the wired network 510. Inboth situations, the receiver 530 is able to support SIC functionalityfor CDMA, as shown in a functional block 531 according to the invention.For example, the receiver 530 is able to perform SIC functionality forCDMA, as shown in a functional block 531, on the signal received fromthe satellite 553. The FIG. 5 shows just one of many embodiments wherethe SIC functionality for CDMA, performed according to the invention,may be performed to provide for improved receiver and systemperformance.

FIG. 6 is a system diagram illustrating an embodiment of a microwavecommunication system 600 that is built according to the invention. Atower transmitter 611 includes a wireless tower 615. The towertransmitter 611, using its wireless tower 615, transmits a signal to atower receiver 612 via a wireless communication channel. The towerreceiver 612 includes a wireless tower 616. The wireless tower 616 isable to receive transmissions from the wireless tower 615 that have beencommunicated via the wireless communication channel. The tower receiver612 is then able to support SIC functionality for CDMA, as shown in afunctional block 633. The FIG. 6 shows just one of many embodimentswhere SIC functionality for CDMA, performed according to the invention,may be performed to provide for improved receiver and systemperformance.

FIG. 7 is a system diagram illustrating an embodiment of apoint-to-point radio communication system 700 that is built according tothe invention. A mobile unit 751 includes a local antenna 755. Themobile unit 751, using its local antenna 755, transmits a signal to alocal antenna 756 via a wireless communication channel. The localantenna 756 is included within a mobile unit 752. The mobile unit 752 isable to receive transmissions from the mobile unit 751 that have beencommunicated via the wireless communication channel. The mobile unit 752is then able to support SIC functionality for CDMA, as shown in afunctional block 753, on the received signal. The FIG. 7 shows just oneof many embodiments where SIC functionality for CDMA, performedaccording to the invention, may be performed to provide for improvedreceiver and system performance.

FIG. 8 is a system diagram illustrating an embodiment of a highdefinition television (HDTV) communication system 800 that is builtaccording to the invention. An HDTV transmitter 810 includes a wirelesstower 811. The HDTV transmitter 810, using its wireless tower 811,transmits a signal to an HDTV set top box receiver 820 via a wirelesscommunication channel. The HDTV set top box receiver 820 includes thefunctionality to receive the wireless transmitted signal. The HDTV settop box receiver 820 is also communicatively coupled to an HDTV display630 that is able to display the demodulated and decoded wirelesstransmitted signals received by the HDTV set top box receiver 820.

The HDTV set top box receiver 820 is then able to support SICfunctionality for CDMA, as shown in a functional block 823 to providefor improved receiver performance. The FIG. 8 shows yet another of manyembodiments where SIC functionality for CDMA, performed according to theinvention, may be performed to provide for improved receiver and systemperformance.

FIG. 9 is a system diagram illustrating an embodiment of a communicationsystem that is built according to the invention. The FIG. 9 showscommunicative coupling, via a communication channel 999, between twotransceivers, namely, between a transceiver 901 and a transceiver 902.The communication channel 999 may be a wired communication channel or awireless communication channel.

Each of the transceivers 901 and 902 includes a transmitter and areceiver. For example, the transceiver 901 includes a transmitter 949and a receiver 940; the transceiver 902 includes a transmitter 959 and areceiver 930. The receivers 940 and 930, within the transceivers 901 and902, respectively, are each operable to support SIC functionality forCDMA according to the invention. This will allow improved signalprocessing for both of the transceivers 901 and 902. For example, thereceiver 940, within the transceiver 901, is able to support SICfunctionality for CDMA, as shown in a functional block 941, on a signalreceived from the transmitter 959 of the transceiver 902. Similarly, thereceiver 930, within the transceiver 902, is able to support SICfunctionality for CDMA, as shown in a functional block 931, on a signalreceived from the transmitter 949 of the transceiver 901. The FIG. 9shows yet another of many embodiments where SIC functionality for CDMA,performed according to the invention, may be performed to provide forimproved receiver performance.

FIG. 10 is a system diagram illustrating another embodiment of acommunication system 1000 that is built according to the invention. TheFIG. 10 shows communicative coupling, via a uni-directionalcommunication channel 1099, between a transmitter 1049 and a receiver1030. The communication channel 1099 may be a wired communicationchannel or a wireless communication channel. The receiver 1030 isoperable to support SIC functionality for CDMA, as shown in a functionalblock 1031, according to the invention. The FIG. 10 shows yet another ofmany embodiments where SIC functionality for CDMA, performed accordingto the invention, may be performed to provide for improved receiver andsystem performance.

FIG. 11 is a system diagram illustrating an embodiment of a CMTS system1100 that is built according to the invention. The CMTS system 1100includes a CMTS medium access controller (MAC) 1130 that operates with anumber of other devices to perform communication from one or more CMs toa WAN 1180. The CMTS MAC 1130 may be viewed as providing the hardwaresupport for MAC-layer per-packet functions including fragmentation,concatenation, and payload header suppression that all are able tooffload the processing required by a system central processing unit(CPU) 1172. This will provide for higher overall system performance. Inaddition, the CMTS MAC 1130 is able to provide support for carrier classredundancy via timestamp synchronization across a number of receivers,shown as a receiver 1111, a receiver 1111, and a receiver 1113 that areeach operable to receive upstream analog inputs. In certain embodiments,each of the receivers 1111, 1112, and 1113 are dual universal advancedTDMA/CDMA (Time Division Multiple Access/Code Division Multiple Access)PHY-layer burst receivers. That is to say, each of the receivers 1111,1112, and 1113 includes at least one TDMA receive channel and at leastone CDMA receive channel; in this case, each of the receivers 1111,1112, and 1113 may be viewed as being multi-channel receivers. In otherembodiments, the receivers 1111, 1112, and 1113 includes only CDMAreceive channels. An embodiment of a receiver including only CDMAreceive channels is shown in FIG. 12.

In addition, the CMTS MAC 1130 may be operated remotely with arouting/classification engine 11 79 that is located externally to theCMTS MAC 1130 for distributed CMTS applications including mini fibernode applications. Moreover, a Standard Programming Interface (SPI)master port may be employed to control the interface to the receivers1111, 1112, and 1113 as well as to a downstream modulator 1120.

The CMTS MAC 1130 may be viewed as being a highly integrated CMTS MACintegrated circuit (IC) for use within the various DOCSIS and advancedTDMA/CDMA physical layer (PHY-layer) CMTS products. The CMTS MAC 1130employs sophisticated hardware engines for upstream and downstreampaths. The upstream processor design is segmented and uses two banks ofSynchronous Dynamic Random Access Memory (SDRAM) to minimize latency oninternal buses. The two banks of SDRAM used by the upstream processorare shown as upstream SDRAM 1175 (operable to support keys andreassembly) and SDRAM 1176 (operable to support Packaging, Handling, andStorage (PHS) and output queues). The upstream processor performs DataEncryption Standard (DES) decryption, fragment reassembly,de-concatenation, payload packet expansion, packet acceleration,upstream Management Information Base (MIB) statistic gathering, andpriority queuing for the resultant packets. Each output queue can beindependently configured to output packets to either a Personal ComputerInterface (PCI) or a Gigabit Media Independent Interface (GMII). DOCSISMAC management messages and bandwidth requests are extracted and queuedseparately from data packets so that they are readily available to thesystem controller.

The downstream processor accepts packets from priority queues andperforms payload header suppression, DOCSIS header creation, DESencryption, Cyclic Redundancy Check (CRC) and Header Check Sequence (ofthe DOCSIS specification), Moving Pictures Experts Group (MPEG)encapsulation and multiplexing, and timestamp generation on the in-banddata. The CMTS MAC 1130 includes an out-of-band generator and CDMAPHY-layer (and/or TDMA PHY-layer) interface so that it may communicatewith a CM device's out-of-band receiver for control of power managementfunctions. The downstream processor will also use SDRAM 1177 (operableto support PHS and output queues). The CMTS MAC 1130 may be configuredand managed externally via a PCI interface and a PCI bus 1171.

Each of the receivers 1111, 1112, and 1113 is operable to support SICfunctionality for CDMA. For example, the receiver 1111 is operable tosupport SIC functionality for CDMA, as shown in a functional block 1191;the receiver 1112 is operable to support SIC functionality for CDMA, asshown in a functional block 1192; and the receiver 1113 is operable tosupport SIC functionality for CDMA, as shown in a functional block 1193.The FIG. 11 shows yet another embodiment in which SIC functionality forCDMA may be performed according to the invention. Any of thefunctionality and operations described in the other embodiments may beperformed within the context of the CMTS system 1100 without departingfrom the scope and spirit of the invention.

FIG. 12 is a system diagram illustrating an embodiment of a burstreceiver system 1200 that is built according to the invention. The burstreceiver system 1200 includes at least one multi-channel receiver 1210.The multi-channel receiver 1210 is operable to receive a number ofupstream analog inputs that are transmitted from CMs. The upstreamanalog inputs may be in the form of either TDMA (Time Division MultipleAccess) and/or CDMA (Code Division Multiple Access) format. A number ofreceive channels may be included within the multi-channel receiver 1210.The FIG. 12 shows a particular embodiment where the multi-channelreceiver 1210 includes a number of CDMA receive channels; however, TDMAreceive channels may also be included.

For example, the multi-channel receiver 1210 is operable to support CDMAreceive channels 1220 (shown as CDMA signal 1 and CDMA signal 2) and tosupport SIC functionality for CDMA, as shown in a functional block 1221,for those received CDMA signals. In addition, the multi-channel receiver1210 is operable to support CDMA receive channels 1230 (shown as CDMAsignal 3 and CDMA signal 4) and to support SIC functionality for CDMA,as shown in a functional block 1231, for those received CDMA signals;the multi-channel receiver 1210 is operable to support CDMA receivechannels 1240 (shown as CDMA signal N and CDMA signal N-1) and tosupport SIC functionality for CDMA, as shown in a functional block 1241,for those received CDMA signals.

Generically speaking, the multi-channel receiver 1210 is operable tosupport a number of receive channels and to support SIC functionalityfor CDMA for those received signals. The multi-channel receiver 1210 ofthe FIG. 12 is operable to interface with a CMTS MAC. The burst receiversystem 1200 may include a number of multi-channel receivers that areeach operable to interface with the CMTS MAC.

In certain embodiments, the multi-channel receiver 1210 provides anumber of various functionalities. The multi-channel receiver 1210 maybe a universal headend advanced TDMA PHY-layer QPSK/QAM (QuadraturePhase Shift Keying/Quadrature Amplitude Modulation) burst receiver; themulti-channel receiver 1210 also include functionality to be a universalheadend advanced CDMA PHY-layer QPSK/QAM burst receiver; or themulti-channel receiver 1210 also include functionality to be a universalheadend advanced TDMA/CDMA PHY-layer QPSK/QAM burst receiver offeringboth TDMA/CDMA functionality. The multi-channel receiver 1210 may beDOCSIS/EuroDOCSIS based, IEEE 802.14 compliant. The multi-channelreceiver 1210 may be adaptable to numerous programmable demodulationincluding BPSK (Binary Phase Shift Keying), and/or QPSK,8/16/32/64/128/256/516/1024 QAM. The multi-channel receiver 1210 isadaptable to support variable symbols rates as well. Other functionalitymay likewise be included to the multi-channel receiver 1210 withoutdeparting from the scope and spirit of the invention. Such variationsand modifications may be made to the communication receiver.

While a particular embodiment of a burst receiver system 1200 isillustrated within the FIG. 12, it is also noted that a continuousreceiver will also support SIC functionality for CDMA according to theinvention. In general, any CDMA receiver may be adapted to support theSIC functionality for CDMA according to the invention.

FIG. 13 is a system diagram illustrating an embodiment of a Bluetooth™communication system 1300 that is built according to the invention. TheBluetooth™ wireless technology is an open specification for asmall-form-factor, low-cost, personal area network connection amongmobile computers, mobile phones and other devices. The Bluetooth™wireless technology specification provides secure, radio-basedtransmission of data and voice. It delivers opportunities for rapid, adhoc, automatic, wireless connections, even when devices are not withinthe line of sight. The Bluetooth™ wireless technology uses a globallyavailable frequency range to ensure interoperability no matter where youtravel.

Bluetooth™ is a standard for a small, cheap radio chip to be pluggedinto computers, printers, mobile phones, etc. A Bluetooth™ chip isdesigned to replace cables by taking the information normally carried bythe cable, and transmitting it at a special frequency to a receiverBluetooth chip, which will then give the information received to thecomputer, phone whatever. In certain embodiments, Bluetooth™communicates on a frequency of 2.45 gigahertz (GHz), which has been setaside by international agreement for the use of industrial, scientificand medical devices (ISM).

The Bluetooth™ wireless technology was developed by the Bluetooth™Special Interest Group, which was founded in 1998 to define anindustry-wide specification for connecting personal and business mobiledevices. More than 1,400 companies are now members of the SpecialInterest Group, signifying the industry's unprecedented acceptance ofthe Bluetooth™ wireless technology.

The FIG. 13 shows a Bluetooth operable device that is operable tocommunicate with another device via a wireless communication channel.The Bluetooth™ operable device may be a computer, printer, and/or mobilephone (or other device) without departing from the scope and spirit ofthe invention. Specifically, the FIG. 13 shows a single chip Bluetooth™2.4 GHz transceiver and baseband device 1310 that is operable to supportSIC functionality for CDMA as shown in a functional block 1311. Fromcertain perspectives, the single chip Bluetooth™ 2.4 GHz transceiver andbaseband device 1310 may be viewed as being a complete single chipBluetooth™ compliant, single chip solution that integrates the 2.4 GHzfractional-N radio transceiver and baseband controller. The 2.4 GHzfractional-N radio transceiver portion is operable to receive a clocksignal from an external clock (say, from a mobile unit) in certainembodiments. The single chip Bluetooth™ 2.4 GHz transceiver and basebanddevice 1310 will provide for a wide range of wireless communication andnetworking applications, including mobile phones, PCs, laptops, PDAs,and other peripheral devices. The other device may be a Bluetooth™device 1350, that may also be operable to support SIC functionality forCDMA as shown in a functional block 1351.

In certain embodiments, a radio section of the single chip Bluetooth™2.4 GHz transceiver and baseband device 1310 incorporates the completereceive and transmit paths, including PLL, VCO, LNA, PA, up-converter,down-converter, modulator, demodulator, and channel select filtering.

The baseband section of the single chip Bluetooth™ 2.4 GHz transceiverand baseband device 1310 controls all Bluetooth™ functionality from thePHY radio to the HCI layer. This includes all bit-level processing,event scheduling, voice/data flow, and on-chip USB/UART/Audio PCMinterfaces (as provided by a USB Port 1321 and a UART Port 1322 that maycommunicatively couple to a host processor 1331, by a PCM Port 1323 thatmay communicatively couple to an audio CODEC 1332). In addition, thesingle chip Bluetooth™ 2.4 GHz transceiver and baseband device 1310 isalso operable to communicatively couple to an (optional) flash memoryvia a processor bus 1323.

The single chip Bluetooth™ 2.4 GHz transceiver and baseband device 1310is a monolithic component implemented in a standard digital CMOSprocess, and requires minimal external components to provide a low-costBOM solution.

It is noted that the single chip Bluetooth™ 2.4 GHz transceiver andbaseband device 1310 within the FIG. 13 shows yet another embodiment ofdevice that is operable to support SIC functionality for CDMA accordingto the invention. Clearly, other Bluetooth™ communication systems mayalso be adapted to support the SIC functionality for CDMA as well.

FIG. 14 is a functional block diagram illustrating an embodiment ofsuccessive interference canceling (SIC) functionality for CDMA 1400 thatis arranged according to the invention in a parallel implementation. Ina block 1401, a spread signal is received from an element 1401 that hasundesirably introduced multipath interference. This multipathinterference may be caused by a variety of sources. For example, onesource of the multipath interference may be from the effects of thecommunication channel itself as shown in a block 1404. However, otherelements that may be employed to compensate for the existence ofnarrowband interference within a signal received by a communicationreceiver; sometimes, these introduced elements actually will introducesome degree of multipath interference. For example, some elements thatare employed to minimize the effects of ingress and/or narrowbandinterference may include an interference cancellation filter (ICF) 1402and/or an interference notch filter 1403. The multipath interferenceelement 1401 may be viewed, at the very least, as being an element thatintroduces multi-path effects into the signal received by the SICfunctionality for CDMA 1400. The attenuation of some of the componentenergy in the signals destroys the perfect orthogonality of the set ofCDMA symbols, which results in ICI. In general, the ICF suppresses or“notch filters” portions of the frequency domain, which is intended toattenuate ingress, but also introduces ICI in the process.

The FIG. 14 shows a functional block diagram of the parallelimplementation of the invention. In this approach, two or moresuccessive interference canceling (SIC) stages are shown by the ICfunctional blocks. The approach also employs a buffer of size M, whichshould be adequate to store the output of the ICF till despread, slice,re-spread, and convolution operations are done. The ICF taps are chosento notch out (or “blank”) any present ingress in the signal. Thecomputation of these taps may be performed using any approach known inthe art.

For example, the signal output by the multipath interference element1401 is simultaneously provided to an interference cancellation (IC)functional block 1410 and a delay element Z^(−M) 1491. When multipleiterations of ICF are to performed using the SIC functionality for CDMA1400, . . . the output of the multipath interference element 1401 isalso simultaneously provided to a delay element Z^(−(N−1)M) 1492 (whenmultiple iterations are performed), and to a delay element Z^(−NM) 1492(when N iterations are performed). The output of the IC functional block1410 may be selected when there is no multipath interference in thereceived signal whatsoever. The IC functional block 1410 includes adespread functional block 1411, a slicer 1412, a re-spread functionalblock 1413, and an ICF-1 functional block 1414 (to perform convolutionoperations) according to the invention; the ICF-1 functional blocksdescribed herein may also be referred to as convolution functionalblocks.

The despread functional block 1411 generates the soft decision of thereceived signal. The slicer 1412 makes a hard decision based on the softdecision provided by the despread functional block 1411. These harddecisions by the slicer 1412 make the decisions offline with no cleaningof the signal; that is to say, without removing any ISI that existsamong the chips. These hard decisions may include a number of errorsthat would be too significant within data applications, but they willgive some accuracy of the received data even though there may be manyerror contained therein. This initial estimate of the data is thenre-spread, in the functional block 1413, to reconstruct the chip levelISI. Then, the operation within the ICF-1 functional block 1414generates the reconstructed ISI (on a chip level) of all of the othertaps besides this first tap.

The functional operations of the functional blocks 1413 and 1414together, is described as partially re-modulating the hard decisions inU.S. Utility Patent application Ser. No. 10/136,059, entitled “CHIPBLANKING AND PROCESSING IN S-CDMA TO MITIGATE IMPULSE AND BURST NOISEAND/OR DISTORTION,” (Attorney Docket No. BP 2058). This is also true forother embodiments described herein that perform similar functionality asthe functional blocks 1413 and 1414.

This result may then be subtracted from the output of the delay elementZ^(−M) 1491. The delay length of the buffer, delay element Z^(−M) 1491,is sufficient to match substantially the time required to perform theoperations within each of the elements of the IC functional block 1410.

This chain of IC functionality may be repeated successively if desiredto provide for even further improved performance. For example, theoutput of the node (the first summing node) where the output of thedelay element Z^(−M) 1491 and the negative output of the IC functionalblock 1410 are summed together may be fed into an IC functional block1420. The IC functional block 1420 will include comparable elements ofthe IC functional block 1410. For example, the IC functional block 1420includes a despread functional block 1421 that generates soft decisionof the output from the first summing node. A slicer 1422 makes a harddecision based on the soft decision provided by the despread functionalblock 1421. These hard decisions by the slicer 1422 make the decisionsoffline with an improved, cleaner signal; that is to say, some of theISI that exists among the chips will have been removed by the operationsdescribed above. These hard decisions will include a fewer number oferrors than in the previous chain of IC functionality. This next 2^(nd)order initial estimate of the data is then re-spread, in a functionalblock 1423, to reconstruct the chip level ISI (which will be reducedwhen compared to the previous chain).

Then, the operation within an ICF-1 functional block 1424 generates thereconstructed ISI (on a chip level) of all of the other taps besidesthis first tap. Functional blocks 1423 and 1424 constitute thegeneration of the partial re-modulated energy described in U.S. Utilitypatent application Ser. No. 10/136,059, entitled “CHIP BLANKING ANDPROCESSING IN S-CDMA TO MITIGATE IMPULSE AND BURST NOISE AND/ORDISTORTION,” (Attorney Docket No. BP 2058).

Again, this reconstructed ISI will be relatively less than in the firstchain. This result may then be subtracted from the output of a delayelement Z^(−(N−1)M) 1492. The delay length of the buffer, delay elementZ^(−(N−1)M) 1492, is sufficient to match substantially the time requiredto perform the operations within each of the elements of the ICfunctional block 1410, within each of the elements of the IC functionalblock 1420, and any additional IC functional blocks that are employed.

It is noted that the resultant output of the slicer 1412 within the ICfunctional block 1410 may be selected as an output. Alternatively, theresultant output of the slicer 1422 within the IC functional block 1420may be selected as an output when it has been determined that a solutionhas been reached (say when a difference between potential output 0 andpotential output 1 are within a predetermined degree of magnitude).Alternatively, this potential output 1 may be selected when apredetermined number of chains (2 in such an embodiment) are selected tobe performed. Another method of determining when to end this process isto look at the Signal to Noise Ratio (SNR) of the signal and to selectthe output from one of the stages when the SNR meets a predeterminedthreshold.

Subsequent chains may be implemented successively as desired to provideeven further performance. For example, multiple chains may be includedup to an IC functional block 1430 (having a de-spread functional block1431, a slicer 1432, a re-spread functional block 1433, and an ICF-1functional block 1434) may also be employed when they are preceded bythe appropriate delay stages. The outputs of each of the slicers 1412,1422, . . . , and 1432 (within the IC functional blocks 1410, 1420, . .. , and 1430) may be selected as outputs using any of the conditionsdescribed above. After the final iteration, the output of the ICfunctional block 1430 is subtracted from the output of the delay elementZ^(−NM) 1493 whose delay is sufficient to match substantially the timerequired to perform the operations within each of the elements of the ICfunctional blocks 1410, 1420, . . . , and 1430. This signal is de-spreadusing the de-spread functional block 1441 to generate soft decisions andthen to a slicer 1442 to generate hard decisions there from; thede-spread functional block 1441 may be viewed as being an outputde-spread functional block and the slicer 1442 may be viewed as being anoutput slicer.

The parallel implementation of the SIC functionality for CDMA 1400 maybe preferable in an application where hardware is not significantlylimited by given design. Other designs, where hardware is much moreconstrained, or more expensive than hardware, may benefit from a serialimplementation described below in FIG. 15.

FIG. 15 is a functional block diagram illustrating an embodiment ofsuccessive interference canceling (SIC) functionality for CDMA 1500 thatis arranged according to the invention in a serial implementation. In ablock 1501, a spread signal is received from an element 1501 that hasundesirably introduced multipath interference. This multipathinterference may be caused by a variety of sources. For example, onesource of the multipath interference may be from the effects of thecommunication channel itself as shown in a block 1504. However, otherelements that may be employed to compensate for the existence ofnarrowband interference within a signal received by a communicationreceiver; sometimes, these introduced elements actually will introducesome degree of multipath interference. For example, some elements thatare employed to minimize the effects of ingress and/or narrowbandinterference may include an interference cancellation filter (ICF) 1502and/or an interference notch filter 1503. The multipath interferenceelement 1501 may be viewed, at the very least, as being an element thatintroduces multi-path effects into the signal received by the SICfunctionality for CDMA 1500. The attenuation of some of the componentenergy in the signals destroys the perfect orthogonality of the set ofCDMA symbols, which results in ICI. In general, the ICF suppresses or“notch filters” portions of the frequency domain, which is intended toattenuate ingress, but also introduces ICI in the process.

The FIG. 15 shows a functional block diagram of the serialimplementation of the invention. In this approach, a single successiveinterference canceling (SIC) stage is shown by an IC functional block1510. The IC functional block 1510 is implemented in such a way that itmay be used over and over again. The FIG. 15 shows an embodiment where asingle IC functional block is employed. Clearly, two IC functionalblocks could also be employed in a ping-pong embodiment as well.

For example, the signal output by the multipath interference element1501 is provided to the IC functional block 1510. The output of the ICfunctional block 1510 (after passing through only once) may be selectedwhen there is no multipath interference in the received signalwhatsoever. The IC functional block 1510 includes a despread functionalblock 1511, a slicer 1512, a re-spread functional block 1513, and anICF-1 functional block 1514 (to perform convolution operations)according to the invention.

The despread functional block 1511 generates the soft decision of thereceived signal. The slicer 1512 makes a hard decision based on the softdecision provided by the despread functional block 1511. These harddecisions by the slicer 1512 make the decisions offline with no cleaningof the signal; that is to say, without removing any ISI that existsamong the chips. These hard decisions may include a number of errorsthat would he too significant within data applications but they willgive some accuracy of the received data even though there may be manyerror contained therein.

This initial estimate of the data is then re-spread, in the functionalblock 1513, to reconstruct the chip level ISI. Then, the operationwithin the ICF-1 functional block 1514 generates the reconstructed ISI(on a chip level) of all of the other taps besides this first tap.

This result (after passing through the IC functional block 1510 onetime) may then be provided to a memory management/processing functionalblock 1591. The original signal, received from the multipathinterference element 1501 has also been stored in a memory 1592 of thememory management/processing functional block 1591 where it has beenbuffered properly using delay elements 1593. The memorymanagement/processing functional block 1591 is also operable to transferand buffer subsequent interference cancelled versions of the signal aswell. Herein, the output from the IC functional block 1510 (afterpassing through one time) is subtracted from the buffered and delayedversion of the original signal using processing functionality 1594; thedelay length of the buffer would be Z^(−M) that is sufficient to matchsubstantially the time required to perform the operations within each ofthe elements of the IC functional block 1510. Multiple, and if desiredselectable, delay elements within the delay elements 1593 may be used toperform provide buffering and delaying of the various versions storedtherein. The memory management/processing functional block 1591 operatesin conjunction with the IC functional block 1510 to perform one, two, .. . , or more iterations of SIC functionality for CDMA using the ICfunctional block 1510 multiple times.

The memory management/processing functional block 1591 is operable toperform buffering (of various sizes M, 2M, and (N−1)M, NM), which shouldbe adequate to store the output of the ICF till despread, slice,re-spread, and convolution operations are done in subsequent iterations.The ICF taps of the ICF-1 functional block 1514 are chosen to notch outany present ingress in the signal in the various iterations. Thecomputation of these taps may be performed using any approach known inthe art. This serial implementation of SIC functionality for CDMA 1500may be repeated successively if desired and may be terminated using anyof the criteria described within the FIG. 14.

Clearly, the resultant will be cleaner for successive iterations thatare performed using the serial implementation of SIC functionality forCDMA 1500 as it will for performing multiple stages of the parallelimplementation of SIC functionality for CDMA 1400. After the finaliteration that is performed, the signal is passed to a despreadfunctional block 1521 and to a slicer 1522 to generate the final outputsignal.

Alternatively, after the final iteration that is performed, the signalis passed to the despread functional block 1511 and to the slicer 1512to generate the final output signal; this way the hardware within the ICfunctional block 1510 may be put to maximum use, and the despreadfunctional block 1521 and the slicer 1522 would not be needed at all.Each of the de-spread functional block 1511 and 1521 may be viewed asbeing an output de-spread functional block, and each of the slicer 1512and 1522 may be viewed as being an output slicer. It is also noted thata combination embodiment may include a portion of the parallelimplementation of the FIG. 14 and a portion of the serial implementationof the FIG. 15 without departing from the scope and spirit of theinvention.

The various embodiments described above within the FIGS. 14 and 15 maybe viewed as those that are operable to deal with systems that are fullysynchronized, in that, the received symbols are not undergoing anyrotation at all. That is to say, these embodiments are operable tosupport SIC functionality for CDMA when no rotation correction and/orcompensation needs to be performed. The potentially disastrous effectsof rotation of received symbols is described using a nominal 30 degreerotation within a variety of constellation types employed within variousmodulations. As will be seen, rotation of the constellation's of lowerorder modulations may sometimes even be tolerated. However, as thenumber of constellation points of the higher order modulations continuesto increase, then the fragility of the modulation becomes such that evenrelatively small amounts of rotation can prove disastrous when trying tomake soft and hard decisions.

FIG. 16 is a diagram illustrating the effects of rotation on symbolscoded using a constellation of QPSK (Quadrature Phase Shift Keying)modulation. On the left hand side, 4 constellation points of a QPSKmodulation are shown as being aligned at 90 degree intervals withrespect to the I,Q axes. On the right hand side, the 4 constellationpoints are shown after having undergone a nominal 30 degree rotation. Ascan been seen in this example, the constellation points still residewithin their original quadrant. Within the QPSK modulation, given thatonly one constellation point is contained within each quadrant, thenthis particular modulation may accommodate relatively small degrees ofrotation.

FIG. 17 is a diagram illustrating the effects of rotation on symbolscoded using a constellation of 8 PSK (8 Phase Shift Keying) modulation.On the left hand side, 8constellation points of an 8 PSK modulation areshown as being aligned at 45 degree intervals with respect to the I.Oaxes. On the right hand side the 8 constellation points are shown afterhaving undergone a nominal 30 degree rotation. As can been seen in thisexample, some of the constellation points no longer reside within theiroriginal quadrant. Perhaps more problematic is the fact that some of theconstellation points now nearly overlap with the positions of whereother constellation points are expected to be located. In thissituation, even a relatively small degree of rotation can be extremelyproblematic.

As the number of constellation points employed within the modulationcontinues to increase, the problems introduced by rotation continue tobe exacerbated.

FIG. 18 is a diagram illustrating the effects of rotation on symbolscoded using a constellation of 16 QAM (Quadrature Amplitude Modulation)modulation. On the left hand side, 16 constellation points of a 16 QAMmodulation are shown as being aligned with respect to the I,Q axes. Onthe right hand side, the 16 constellation points are shown after havingundergone a nominal 30 degree rotation. As can been seen in thisexample, some of the constellation points no longer reside within theiroriginal quadrant. Perhaps more problematic is the fact that several ofthe constellation points almost overlap with the positions of whereother constellation points are expected to be located. Given that thereare 16 constellation points involved, the negative effects introduced bythe rotation are extreme. In this situation, even a relatively smalldegree of rotation is extremely problematic.

FIG. 19 is a diagram illustrating the effects of rotation on symbolscoded using a constellation of 16 APSK (Amplitude Phase Shift Keying)modulation. On the left hand side, 16 constellation points of a 16 APSKmodulation are shown as being aligned with respect to the I,Q axes. Onthe right hand side, the 16 constellation points are shown after havingundergone a nominal 30 degree rotation. Again, as can been seen in thisexample, some of the constellation points no longer reside within theiroriginal quadrant. Similar to the 16 QAM example, perhaps moreproblematic is the fact that several of the constellation points almostoverlap with the positions of where other constellation points areexpected to be located. Also similar to the 16 QAM example, given thatthere are 16 constellation points involved, the negative effectsintroduced by the rotation are extreme. In this situation, even arelatively small degree of rotation is extremely problematic.

It is also understood that even higher order modulations will suffereven more greatly from the effects of rotation. For example, thedegradation of performance of constellation points of a 256 QAM or 1024QAM modulation could be even greater given that even more constellationpoints may nearly overlap and interfere with one another. Performingaccurate soft and hard decisions will be virtually impossible.

FIG. 20 is a functional block diagram illustrating an embodiment ofsuccessive interference canceling (SIC) functionality for CDMA that isarranged according to the invention in a parallel implementation that isoperable to compensate for rotation. In a block 2001, a spread signal isreceived from an element 2001 that has undesirably introduced multipathinterference. This multipath interference may be caused by a variety ofsources. For example, one source of the multipath interference may befrom the effects of the communication channel itself as shown in a block2004. However, other elements that may be employed to compensate for theexistence of narrowband interference within a signal received by acommunication receiver; sometimes, these introduced elements actuallywill introduce some degree of multipath interference. For example, someelements that are employed to minimize the effects of ingress and/ornarrowband interference may include an interference cancellation filter(ICF) 2002 and/or an interference notch filter 2003. The multipathinterference element 2001 may be viewed, at the very least, as being anelement that introduces multi-path effects into the signal received bythe SIC functionality for CDMA 2000. The attenuation of some of thecomponent energy in the signals destroys the perfect orthogonality ofthe set of CDMA symbols, which results in ICI. In general, the ICFsuppresses or “notch filters” portions of the frequency domain, which isintended to attenuate ingress, but also introduces ICI in the process.

The FIG. 20 shows a functional block diagram of the parallelimplementation of the invention that is operable to compensate forrotation. In this approach, two or more successive interferencecanceling (SIC) stages are shown by the IC functional blocks, and eachof those IC functional blocks is operable to compensate for rotation ofthe symbols within the received signal. The approach also employs abuffer of size M, which should be adequate to store the output of theICF till despread, derotate, slice, rerotate, re-spread, and convolutionoperations are done. The ICF taps are chosen to notch out (or “blank”)any present ingress in the signal. The computation of these taps may beperformed using any approach known in the art.

For example, the signal output by the multipath interference element2001 is simultaneously provided to an interference cancellation (IC)functional block 2010 and a delay element Z⁻M 2091. When multipleiterations of ICF are to performed using the SIC functionality for CDMA2000, . . . the output of the multipath interference element 2001 isalso simultaneously provided to a delay element Z^(−(N−1)M) 2092 (whenmultiple iterations are performed), and to a delay element Z^(−NM) 2092(when N iterations are performed). The output of the IC functional block2010 may be selected when there is no multipath interference in thereceived signal whatsoever. The IC functional block 2010 includes adespread functional block 2011, a slicer 2012, a re-spread functionalblock 2013, and an ICF-1 functional block 2014 (to perform convolutionoperations) according to the invention.; the ICF-1 functional blocksdescribed herein may also be referred to as convolution functionalblocks.

The despread functional block 2011 generates the soft decision of thereceived signal. The output of the despread functional block 2011 issimultaneously passed to a parameter estimator 2019 and a derotator2016. The parameter estimator 2019 may employ preamble processingthereby using known and expected symbols to perform the rotationestimation of the received signal. Alternatively, the parameterestimator 2019 may also employ a portion of the payload (or data) of areceived data segment as well. Once an actual estimation of the rotationis made, then the parameter estimator provides this rotation estimate tothe derotator 2016. The derotator 2016 may include a buffer that matchesthe time period in which the parameter estimator 2019 takes to performits estimation of the rotation within the signal. In addition, theparameter estimator provides this rotation estimate to the rerotator2018 that is operable to add the rotation back into the signal, afterslicing has been performed by the slicer 2012, for subsequent iterationsof the SIC functionality for CDMA.

The slicer 2012 makes a hard decision based on the soft decisionprovided by the despread functional block 2011. These hard decisions bythe slicer 2012 make the decisions offline with no cleaning of thesignal; that is to say, without removing any ISI that exists among thechips. These hard decisions may include a number of errors that would betoo significant within data applications, but they will give someaccuracy of the received data even though there may be many errorcontained therein.

This initial estimate of the data is then passed to the rerotator 2018and then this result is re-spread, in the functional block 2013, toreconstruct the chip level ISI. Then, the operation within the ICF-1functional block 2014 generates the reconstructed ISI (on a chip level)of all of the other taps besides this first tap. This result may then besubtracted from the output of the delay element Z^(−M) 2091. The delaylength of the buffer, delay element Z^(−M) 2091, is sufficient to matchsubstantially the time required to perform the operations within each ofthe elements of the IC functional block 2010.

This chain of IC functionality, including parameter estimation directedderotation and rerotation, may be repeated successively if desired toprovide for even further improved performance. For example, the outputof the node (the first summing node) where the output of the delayelement Z^(−M) 2091 and the negative output of the IC functional block2010 are summed together may be fed into an IC functional block 2020.The IC functional block 2020 will include comparable elements of the ICfunctional block 2010. For example, the IC functional block 2020includes a despread functional block 2021 that generates soft decisionof the output from the first summing node. Similarly, a parameterestimator 2029, a derotator 2026, and a rerotator 2028 all operate, insimilar manner to the parameter estimator 2019, the derotator 2016, andthe rerotator 2018 of the IC functional block 2010, to compensate forany rotation within the signal at this point within the processing.

After the signal passes through the derotator 2026, a slicer 2022 makesa hard decision based on the soft decision provided by the despreadfunctional block 2021. These hard decisions by the slicer 2022 make thedecisions offline with an improved, cleaner signal; that is to say, someof the ISI that exists among the chips will have been removed by theonerations described above. These hard decisions will include a fewernumber of errors than in the previous chain of IC functionality.

This next 2^(nd) order initial estimate of the data is then passed tothe rerotator 2028 and then this result is then re-spread, in afunctional block 2023, to reconstruct the chip level ISI (which will bereduced when compared to the previous chain).

Then, the operation within a ICF-1 functional block 2024 generates thereconstructed ISI (on a chip level) of all of the other taps besidesthis first tap; again, this reconstructed ISI will be relatively lessthan in the first chain. This result may then be subtracted from theoutput of a delay element Z^(−(N−1)M) 2092. The delay length of thebuffer, delay element Z^(−(N−1)M) 2092, is sufficient to matchsubstantially the time required to perform the operations within each ofthe elements of the IC functional block 2010, within each of theelements of the IC functional block 2020, and any additional ICfunctional blocks that are employed.

It is noted that the resultant output of the slicer 2012 within the ICfunctional block 2010 may be selected as an output. Alternatively, theresultant output of the slicer 2022 within the IC functional block 2020may be selected as an output when it has been determined that a solutionhas been reached (say when a difference between potential output 0 andpotential output 1 are within a predetermined degree of magnitude).Alternatively, this potential output 1 may be selected when apredetermined number of chains (2 in such an embodiment) are selected tobe performed. Another method of determining when to end this process isto look at the Signal to Noise Ratio (SNR) of the signal and to selectthe output from one of the stages when the SNR meets a predeterminedthreshold.

Subsequent chains may be implemented successively as desired to provideeven further performance. For example, multiple chains may be includedup to perform even additional SIC functionality for CDMA according tothe invention.

After the final iteration, the output of the IC functional block 2020 issubtracted from the output of the delay element Z^(−NM) 2093 whose delayis sufficient to match substantially the time required to perform theoperations within each of the elements of the IC functional blocks 2010,2020, . . . , and any other IC functional blocks. This signal isde-spread using the de-spread functional block 2041 to generate softdecisions. This result is then passed simultaneously to a parameterestimator 2049 and a derotator 2046. The output from the derotator 2046is then passed to a slicer 2042 to generate hard decisions there from;the de-spread functional block 2041, along with the parameter estimator2049 and the derotator 2046, may be viewed as being the outputprocessing functional blocks associated with the slicer 2042 to generatean output, namely, the potential output N.

The parallel implementation of the SIC functionality for CDMA 2000 maybe preferable in an application where hardware is not significantlylimited by given design and compensating for rotation in the receivedsignal is a design criteria or consideration. Other designs, wherehardware is much more constrained, or more expensive than hardware, maybenefit from a serial implementation described below in FIG. 21 that isalso operable to perform derotation and rerotation.

FIG. 21 is a functional block diagram illustrating an embodiment of SICfunctionality for CDMA that is arranged according to the invention in aserial implementation that is operable to compensate for rotation. In ablock 2101, a spread signal is received from an element 2101 that hasundesirably introduced multipath interference. This multipathinterference may be caused by a variety of sources. For example, onesource of the multipath interference may be from the effects of thecommunication channel itself as shown in a block 2104. However, otherelements that may be employed to compensate for the existence ofnarrowband interference within a signal received by a communicationreceiver; sometimes, these introduced elements actually will introducesome degree of multipath interference. For example, some elements thatare employed to minimize the effects of ingress and/or narrowbandinterference may include an interference cancellation filter (ICF) 2102and/or an interference notch filter 2103. The multipath interferenceelement 2101 may be viewed, at the very least, as being an element thatintroduces multi-path effects into the signal received by the SICfunctionality for CDMA 2100. The attenuation of some of the componentenergy in the signals destroys the perfect orthogonality of the set ofCDMA symbols, which results in ICI. In general, the ICF suppresses or“notch filters” portions of the frequency domain, which is intended toattenuate ingress, but also introduces ICI in the process.

The FIG. 21 shows a functional block diagram of the serialimplementation of the invention that is operable to compensate forrotation. In this approach, a single successive interference canceling(SIC) stage is shown by an IC functional block 2110. The IC functionalblock 2110 is implemented in such a way that it may be used over andover again. The FIG. 21 shows an embodiment where a single IC functionalblock is employed. Clearly, two IC functional blocks could also beemployed in a ping-pong embodiment as well without departing from thescope and spirit of the invention.

For example, the signal output by the multipath interference element2101 is provided to the IC functional block 2110. The output of the ICfunctional block 2110 (after passing through only once) may be selectedwhen there is no multipath interference in the received signalwhatsoever. The IC functional block 2110 includes a despread functionalblock 211 1, a parameter estimator 2119, a derotator 2116, a slicer2112, a rerotator 2118, a re-spread functional block 2113, and an ICF-1functional block 2114 (to perform convolution operations) according tothe invention. The elements within the IC functional block 2110 operatecooperatively in a similar fashion to the IC functional blocks withinthe FIG. 20.

The despread functional block 2111 generates the soft decision of thereceived signal. The output of the despread functional block 2111 issimultaneously provided to the parameter estimator 2119 and thederotator 2116. The slicer 2112 makes a hard decision based on the softdecision provided by the derotator 2116 after having passed through thedespread functional block 2111. These hard decisions by the slicer 2112may be made offline with no cleaning of the signal; that is to saywithout removing any ISI that exists among the chips. These harddecisions may include a number of errors that would be too significantwithin data applications, but they will give some accuracy of thereceived data even though there may be many error contained therein.This initial estimate of the data is passed to the rerotator 2118 andthen this result is then re-spread, in the functional block 2113, toreconstruct the chip level ISI. Then, the operation within the ICF-1functional block 2114 generates the reconstructed ISI (on a chip level)of all of the other taps besides this first tap.

This result (after passing through the IC functional block 2110 onetime) may then be provided to a memory management/processing functionalblock 2191. The original signal, received from the multipathinterference element 2101 has also been stored in a memory 2192 of thememory management/processing functional block 2191 where it has beenbuffered properly using delay elements 2193. The memorymanagement/processing functional block 2191 is also operable to transferand buffer subsequent interference cancelled versions of the signal aswell. Herein, the output from the IC functional block 2110 (afterpassing through one time) is subtracted from the buffered and delayedversion of the original signal using processing functionality 2194; thedelay length of the buffer would be Z^(−M) that is sufficient to matchsubstantially the time required to perform the operations within each ofthe elements of the IC functional block 2110. Multiple, and if desiredselectable, delay elements within the delay elements 2193 may be used toperform provide buffering and delaying of the various versions storedtherein. The memory management/processing functional block 2191 operatesin conjunction with the IC functional block 2110 to perform one, two, .. . , or more iterations of SIC functionality for CDMA using the ICfunctional block 2110 multiple times.

The memory management/processing functional block 2191 is operable toperform buffering (of various sizes M, 2M, . . . , and (N−1)M, NM),which should be adequate to store the output of the ICF till despread,derotated, slice, rerotated, re-spread, and convolution operations aredone in subsequent iterations. The ICF taps of the ICF-1 functionalblock 2114 are chosen to notch out any present ingress in the signal inthe various iterations. The computation of these taps may be performedusing any approach known in the art. This serial implementation of SICfunctionality for CDMA 2100 may be repeated successively if desired andmay be terminated using any of the criteria described within the FIG.20.

Clearly, the resultant will be cleaner for successive iterations thatare performed using the serial implementation of SIC functionality forCDMA 2100 as it will for performing multiple stages of the parallelimplementation of SIC functionality for CDMA 2000 that is also operableto correct for rotation. After the final iteration that is performed,the signal is passed to a despread functional block 2121, to a parameterestimator 2129 and a derotator 2126, and then to a slicer 2122 togenerate the final output signal.

Alternatively, after the final iteration that is performed, the signalis passed to the despread functional block 2111, to the derotator 2116,and to the slicer 2112 to generate the final output signal; this way thehardware within the IC functional block 2110 may be put to maximum use,and the despread functional block 2121 and the slicer 2122 would not beneeded at all. Each of the de-spread functional block 2111/derotator2116 and the de-spread functional block 2121/derotator 2126 may beviewed as being the output functional blocks that operate cooperativelywith the slicers 2112 and 2122 to generate the final potential outputs.It is also noted that a combination embodiment may include a portion ofthe parallel implementation of the FIG. 20 and a portion of the serialimplementation of the FIG. 21 without departing from the scope andspirit of the invention.

The various embodiments described above within the FIGS. 20 and 21 maybe viewed as those that are operable to deal with systems that are notfully synchronized, in that, the received symbols may actually haveundergone some rotation. That is to say, these embodiments are operableto support SIC functionality for CDMA when rotation correction and/orcompensation may need to be performed.

FIG. 22 is an operational flow diagram illustrating an embodiment of anSIC method for CDMA 2200 that is performed according to the invention.In a block 2210, a signal is received that has some degree ofinterference contained therein. In a block 2220, the signal is despreadand soft decisions are made of the despread signal. These soft decisionsare sliced as shown in a block 2230 thereby generating hard decisions.Clearly, some of these hard decisions may include some errors, giventhat no SIC functionality for CDMA has yet to be made on the signal.Then, in a block 2240, these hard decisions are re-spread. The ICF tapsof an ICF are chosen in a block 2250, using any manner known in the art,that will subsequently be used to convolve the hard decisions (allexcept the first tap) as shown in a block 2260. This convolved signal,output of an ICF-1 functional block, is then subtracted from thebuffered and delayed version of the original signal as shown in a block2270.

This process may be performed successively. The SIC method for CDMA 2200may terminate when it has been determined that a solution has beenreached (say when a difference between one iteration and a subsequentiteration are within a predetermined degree of magnitude).Alternatively, a predetermined number of iterations may be performed inevery case (this number of iterations may be selectable andprogrammable). Another method of determining when to end this process isto look at the Signal to Noise Ratio (SNR) of the signal and to selectthe output from one of the stages when the SNR meets a predeterminedthreshold.

After the total number of iterations has been performed according to theFIG. 24, the final output signal is then de-spread thereby generatingsoft decisions and sliced to generate the final output hard decisions.This may be performed using any of the various embodiments describedherein.

FIG. 23 is an operational flow diagram illustrating another embodimentof an SIC method for CDMA 2300 that is performed according to theinvention. In a block 2310, a signal is received that has some degree ofinterference contained therein. In a block 2220, the signal is despreadand soft decisions are made of the despread signal. In a block 2322,parameter estimation is made on this signal in an effort to estimate therotation of the symbols within the received signal. This may beperformed using preamble processing in certain embodiments.Alternatively, this may be performed using a portion of the payload (ordata) of a received data segment as well. After the estimate of therotation is made, then any rotation within the signal is then derotatedas shown in a block 2324. Then, this result then undergoes slicing asshown in a block 2230 thereby generating hard decisions. In someembodiments, the signal at this point is taken as the final outputsignal. However, it is noted that some of these hard decisions mayinclude some errors, given that no SIC functionality for CDMA has yet tobe made on the signal. However, within embodiments that do not take thesignal at this point as the final output and where multiple iterationsare performed, any rotation that has been derotated is then rerotatedback into the signal at this point as shown in a block 2332.

Then, in a block 2340, these hard decisions, that do include anyrotation having been rerotated back in, are re-spread. The ICF taps ofan ICF are chosen in a block 2350, using any manner known in the art,that will subsequently be used to convolve the hard decisions (allexcept the first tap) as shown in a block 2360. This convolved signal,output of an ICF-1 functional block, is then subtracted from thebuffered and delayed version of the original signal as shown in a block2370.

This process may be performed successively. The SIC method for CDMA 2300may terminate when it has been determined that a solution has beenreached (say when a difference between one iteration and a subsequentiteration are within a predetermined degree of magnitude).Alternatively, a predetermined number of iterations may be performed inevery case (this number of iterations may be selectable andprogrammable). Another method of determining when to end this process isto look at the Signal to Noise Ratio (SNR) of the signal and to selectthe output from one of the stages when the SNR meets a predeterminedthreshold.

After the total number of iterations has been performed according to theFIG. 23, the final output signal is then de-spread thereby generatingsoft decisions and sliced to generate the final output hard decisions.This may be performed using any of the various embodiments describedherein.

FIG. 24 is a diagram illustrating a number of considerations of whichiteration(s) to perform rotation correction according to the invention.One determination may be made based on the type of modulation that isemployed. For example, those modulations that employ fewer numbers ofconstellation points may not need as much rotation correction, if any atall, as those that employ higher numbers of constellation points.

Another consideration may be based on what processing type is employedto perform rotation estimation. For example, some embodiments may employpreamble processing that employs only the preamble symbols of a receivedsignal. Other embodiments may employ both the preamble and any payloadas well. There may be a system may not include sufficient processingresources to perform preamble and payload processing every time. Withinsome iterations, the system may perform rotation correction, but it maynot in all of the iterations.

Yet another consideration may be based on a predetermined order of whichiterations should undergo rotation correction. For example, someembodiments perform rotation correction at every iteration including thebeginning, the middle, and the end. Other embodiments will performrotation correction only at the beginning, or only at the end.

Yet another consideration is the magnitude of the rotation error. Whenthe magnitude exceeds a particular threshold, then the rotationcorrection may be performed according to the invention. When themagnitude does not exceed that particular threshold, then the rotationcorrection need not be performed according to the invention. Inaddition, the consideration may be adaptive in nature. This may involveconsidering either one or both of the system operating conditions andthe availability of processing resources that may be capable to performthe rotation correction.

FIG. 25 shows an embodiment of SIC for CDMA simulation results accordingto the invention. The FIG. 25 show simulation results for despreaderoutput constellations of three SIC iterations in an SCDMA system with120 active codes and QPSK (Quadrature Phase Shift Keying) modulation,which uses an ICF whose tap magnitudes are shown in the upper right handside of FIG. 25. The lower right hand side of FIG. 25 shows the harddecision SER versus the SIC iteration (i=0, for no SIC, and when i=1, 2,3, 4, and 5). The FIG. 25 show that the SIC procedure according to theinvention converges, in this case, in 3 iterations. Again, the number ofiterations to be performed may be selected appropriately for the givensituation. The number of iterations may be predetermined, it may bedetermined based upon convergence of the constellation points, and/or itmay be determined by looking at some measurand such as SNR in thereceived signal after having undergone various iterations of SIC forCDMA.

In view of the above detailed description of the invention andassociated drawings, other modifications and variations will now becomeapparent. It should also be apparent that such other modifications andvariations may be effected without departing from the spirit and scopeof the invention.

1. A communication device, comprising: an interference cancellationfilter that is operable to reduce ingress or narrowband interferencewithin a signal thereby generating a filtered signal, wherein theinterference cancellation filter generates inter-code interferencewithin the signal; and an interference cancellation functional block isoperable to de-spread, slice, re-spread, and convolve the filteredsignal thereby generating a convolved signal, wherein the convolution ofthe signal is operable to reproduce the inter-code interferencegenerated by the interference cancellation filter; and wherein: theconvolved signal is combined with the filtered signal thereby generatinga cleaned signal.
 2. The communication device of claim 1, furthercomprising: an output de-spread functional block that is operable togenerate a plurality of output soft decisions from the cleaned signal;and an output slicer that is operable to generate a plurality of outputhard decisions using the plurality of output soft decisions.
 3. Thecommunication device of claim 1, further comprising: a delay elementthat is operable to delay the filtered signal for a period of timesubstantially matching a time the filtered signal is processed withinthe interference cancellation functional block; and wherein: theconvolved signal is subtracted from a delayed output signal that isprovided from the delay element thereby generating the cleaned signal.4. The communication device of claim 1, wherein: the interferencecancellation filter employs a selected plurality of interferencecancellation filter taps to notch out ingress or narrowband interferencewithin the signal thereby generating the filtered signal.
 5. Thecommunication device of claim 1, wherein: the interference cancellationfunctional block includes a de-spread functional block, a slicer, are-spread functional block, and a convolution functional block; thede-spread functional block is operable to de-spread the filtered signalthereby generating a de-spread signal; the slicer is operable to slicethe de-spread signal thereby generating a sliced signal; the re-spreadfunctional block is operable to re-spread the sliced signal therebygenerating a re-spread signal; and the convolution functional block isoperable to convolve the re-spread signal, that involves reproducing theinter-code interference generated by the interference cancellationfilter, thereby generating the convolved signal.
 6. The communicationdevice of claim 1, wherein: the signal is launched into a communicationchannel by at least one additional communication device; thecommunication device is operable to receive the signal from thecommunication channel; before launching the signal into thecommunication channel, the at least one additional communication devicemaps a symbol to a constellation point within a constellation: as thesignal is transmitted from the at least one additional communicationdevice to the communication device via the communication channel, thesignal is affected such that the symbol undergoes rotation with respectto the constellation to which it is mapped; and the communication deviceincludes a derotator that is operable to compensate for the rotation. 7.The communication device of claim 1, wherein: the communication deviceincludes a derotator that is operable to compensate for any rotation ofa constellation to which a symbol of the signal is mapped; and theconstellation includes a plurality of constellation points.
 8. Thecommunication device of claim 1, wherein: the interference cancellationfunctional block includes a convolution functional block; theconvolution functional block is operable to estimate the inter-codeinterference generated by the interference cancellation filter; and theconvolution functional block is operable to convolve the re-spreadsignal that involves reproducing at least some of the inter-codeinterference generated by the interference cancellation filter, therebygenerating the convolved signal.
 9. The communication device of claim 1,further comprising: at least one additional interference cancellationfunctional block is operable to de-spread, slice, re-spread, andconvolve the cleaned signal thereby generating at least one additionalconvolved signal; and wherein: the at least one additional convolvedsignal is combined with the filtered signal thereby generating at leastone additional cleaned signal.
 10. The communication device of claim 1,further comprising: at least one additional interference cancellationfunctional block is operable to de-spread, slice, re-spread, andconvolve the cleaned signal thereby generating at least one additionalconvolved signal; and wherein: the at least one additional convolvedsignal is combined with the filtered signal thereby generating at leastone additional cleaned signal; the communication device is operable tocompare the cleaned signal and the at least one additional cleanedsignal; and the communication device selects either the cleaned signalor the at least one additional cleaned signal based on a differencebetween the cleaned signal and the at least one additional cleanedsignal.
 11. The communication device of claim 1, wherein: thecommunication device is implemented within a wireless communicationsystem.
 12. A communication device, comprising: an interferencecancellation filter that is operable to reduce ingress or narrowbandinterference within a signal thereby generating a filtered signal,wherein the interference cancellation filter generates inter-codeinterference within the signal; and an interference cancellationfunctional block includes a de-spread functional block, a derotator, aslicer, a rerotator, a re-spread functional block, and a convolutionfunctional block; and wherein: the de-spread functional block isoperable to de-spread the filtered signal thereby generating a de-spreadsignal; the derotator is operable to operable to compensate for anyrotation of a constellation to which a symbol of the signal is mappedthereby generating a derotated signal; the slicer is operable to slicethe derotated signal thereby generating a sliced signal; the rerotatoris operable to operable to reintroduce the rotation of the constellationinto the sliced signal thereby generating a rerotated signal; there-spread functional block is operable to re-spread the rerotated signalthereby generating a re-spread signal; the convolution functional blockis operable to convolve the re-spread signal to reproduce the inter-codeinterference generated by the interference cancellation filter therebygenerating a convolved signal; and the convolved signal is combined withthe filtered signal thereby generating a cleaned signal.
 13. Thecommunication device of claim 12, further comprising: a parameterestimator that is operable to estimate any rotation of the constellationto which the symbol of the signal is mapped.
 14. The communicationdevice of claim 12, further comprising: at least one additionalinterference cancellation functional block is operable to de-spread,derotate, slice, rerotate, re-spread, and convolve the cleaned signalthereby generating at least one additional convolved signal; andwherein: the at least one additional convolved signal is combined withthe filtered signal thereby generating at least one additional cleanedsignal.
 15. The communication device of claim 12, further comprising: atleast one additional interference cancellation functional block isoperable to de-spread, derotate, slice, rerotate, re-spread, andconvolve the cleaned signal thereby generating at least one additionalconvolved signal; and wherein: the at least one additional convolvedsignal is combined with the filtered signal thereby generating at leastone additional cleaned signal; the communication device is operable tocompare the cleaned signal and the at least one additional cleanedsignal; and the communication device selects either the cleaned signalor the at least one additional cleaned signal based on a differencebetween the cleaned signal and the at least one additional cleanedsignal.
 16. The communication device of claim 12, wherein: thecommunication device is implemented within a wireless communicationsystem.
 17. A method for performing interference cancellation within asignal, the method comprising: filtering a signal to reduce ingress ornarrowband interference within the signal thereby generating a filteredsignal, wherein the filtering generates inter-code interference withinthe signal; de-spreading the filtered signal thereby generating ade-spread signal; slicing the de-spread signal thereby generating asliced signal; re-spreading the sliced signal thereby generating are-spread signal; convolving the re-spread signal, that includesreproducing the inter-code interference generated by the interferencecancellation filter, thereby generating a convolved signal; andcombining with the filtered signal thereby generating a cleaned signal.18. The method of claim 17, further comprising: generating a pluralityof output soft decisions from the cleaned signal; and slicing theplurality of output soft decisions thereby generating a plurality ofoutput hard decisions.
 19. The method of claim 17, further comprising:compensating for any rotation of a constellation to which a symbol ofthe signal is mapped.
 20. The method of claim 17, wherein: the method isperformed within a communication device: and the communication device isimplemented within a wireless communication system.